Enhancement of setting times and hardening of alkali-activated slag binder using CO2-modified slag

Alkali-activated slag (AAS) has been widely studied owing to its excellent performance; however, its rapid setting hinders its development. This study demonstrates that CO2 exposure, a simple and environmentally friendly pretreatment method for slag, inhibits the early reaction of slag and then manages the setting behavior of AAS. The role of CO2-modified slag during the alkali-activation process was investigated via setting time, pore solution, and hydration exothermic analysis of AAS. CO2 adsorption on slag mainly forms amorphous carbonate. The presence of carbonates reduces the reactivity of slag and delays the dissolution rate of Ca, Si, and Al from slag in the early period, resulting in a prolonged setting time. The specific effects of CO2-modified slag on the setting behavior of AAS depend on the duration in which slag is exposed to CO2. The initial setting time of waterglass-activated modified-slag increased by 19–145 times, whereas the compressive strength remained unchanged.